1. Field of the Invention
Embodiments of the prevent invention relate to a tandem-type electrophotographic image forming apparatus and a process cartridge incorporated therein, and more particularly to a tandem-type electrophotographic image forming apparatus that can frequently print monochrome (black-and-white) images as well as color images and a process cartridge incorporated therein.
2. Description of the Related Art
Tandem-type color image forming apparatuses produce monochrome images (e.g., black-and-white images) as well as color images. Monochrome images are generally printed more frequently than color images, and therefore a photoconductor provided for forming black images can cause mechanical wear relatively easily, as compared to the other photoconductors provided for forming other color images. To address the drawback, various techniques have been considered to extend a life of a black photoconductor to be longer than the other color photoconductors used in a same tandem-type color image forming apparatus.
Regardless of tandem-type image forming apparatuses, energy-saving devices are demanded and needed recently with concerns about the environment. Most of the power used for an image forming apparatus is consumed in a fixing process for fixing a toner image to a recording medium, and therefore a fixing unit and/or toner have been developed to reduce the amount of power consumption.
For example, Japanese Patent Application Publication No. JP 2008-134304 discloses an image forming apparatus that can prevent the extremely short life tendency of a specific (black) electrostatic latent image carrier (photoconductor) by replacing multiple electrostatic latent image carriers at similar intervals or cycles to each other. The image forming apparatus disclosed in Japanese Patent Application Publication No. JP 2008-134304 includes a plurality of electrostatic latent image holders, contact charging means, and a non-contact charging means. The electrostatic latent image holders are formed by stacking a plurality of functional layers, and the component ratio of the respective functional layers of the electrostatic latent image holders corresponding to the contact charging means and the component ratio of the respective functional layers of the electrostatic latent image holder corresponding to the non-contact charging means are different.
By forming the black image forming unit different from the other color image forming units, the image forming apparatus disclosed in Japanese Patent Application Publication No. JP 2008-134304 prevents the life of the black image forming unit from being extremely shortened. Since the same image forming unit is used in a color image printing mode and in a monochrome image printing mode, in a case in which a user prints an extremely large amount of monochrome images, the black image forming unit needs to be replaced at cycles different from the other image forming units.
On the other hand, as described above, to respond to the needs for energy-saving to solve the environmental issued, it is desired to reduce the amount of consumption of power required for operations performed in the image forming apparatus as much as possible.